Existing requirements for providing precision approach and landing navigation during flight for both commercial and military aircraft include accuracy, integrity, availability, and continuity of function. Traditionally, location determination incorporates the use of global positioning system (GPS)-based satellite navigation that can provide accuracy down to the centimeter level. Integrity of the navigation system is typically expressed in terms of confidence levels. The higher the confidence level, the more reliable the information provided. Availability and continuity provide assurances that the system will be available not only at the beginning of the operation, but throughout the entire duration of the flight.
Meeting these requirements is especially crucial for autonomous shipboard landings on seaborne aircraft carriers. Proposals of using GPS to generate relative navigation and guidance to meet these challenges can provide the accuracy and integrity required, however, a shipboard approach and landing is more demanding than typical land-based approaches and landings. Aircraft navigation systems used in a shipboard approach and landing must continue to meet the requirements listed above even at sea under severe weather conditions and demanding electromagnetic environments. This is particularly important when landing on an aircraft carrier, where vertical landing errors of more than 0.3 meters is unacceptable and can result in unsafe landing conditions.
Some of the factors to consider during autonomous shipboard landings are a lack of visibility, operating under combat conditions, and a dynamically changing touchdown point. Another factor to consider is that any type of navigational aid must include velocity determination, since both the aircraft and the aircraft carrier are in motion relative to one another. In addition to low rate GPS measurement data other, higher rate, measurements are needed in order to evaluate the relative state between aircraft and aircraft carrier, i.e., the aircraft's position and velocity with respect to the moving runway and touchdown point, as accurately as possible during a precision approach and landing. Existing navigational aids include using an inertial navigation system (INS) to measure the position and altitude of the approaching aircraft in conjunction with GPS. With a combination GPS/INS solution, the short-term measurement data from the INS, which is susceptible to drift errors over time, is corrected by the exact location and time references provided by satellite navigation. In addition, since INS operates in reference to the inertial movements of the system, it is immune to detection or jamming.
GPS-only methods of relative navigation, however, are susceptible to jamming (intentional) and interference (unintentional) which can severely impact the operation. For example, loss of the GPS navigational signal as the aircraft is nearing the landing area could result in a devastating loss. Moreover, current ship-based methods do not always provide a secure transmission link, leaving either the aircraft or aircraft carrier vulnerable to detection.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for an improved method of avionic navigation.